The present invention relates to an aqueous emulsion of a high-polymeric organopolysiloxane of the oil-in-water type having excellent stability of emulsion or, more particularly, to an oil-in-water aqueous emulsion of an organopolysiloxane suitable for use as an adjuvant in various kinds of toiletry and cosmetic preparations and for use in other applications.
It is a well established technology that an aqueous emulsion of an organopolysiloxane is used as an additive ingredient in a wide variety of compositions including toiletry and cosmetic preparations, polishing agents, mold-release agents, fabric-finishing agents and others. In particular, hair-care treatment toiletry preparations are, in many cases, formulated with such an organopolysiloxane emulsion as an adjuvant of which the organopolysiloxane contained in the aqueous emulsion should have an average degree of polymerization or viscosity as high as possible because the adherence of the organopolysiloxane to the surface of the hair treated with the hair-care treatment preparation can be improved as the average degree of polymerization of the organopolysiloxane is increased as compared with an organopolysiloxane of a low degree of polymerization or low viscosity.
For example, Japanese Patent Kokai 4-36226 and 4-224309 propose a formulation of a shampoo composition with admixture of an aqueous emulsion of a high-polymeric organopolysiloxane. According to the disclosures therein, the foamability of the shampoo composition is never or little affected when the organopolysiloxane droplets as the dispersed phase in the aqueous emulsion added thereto have a particle diameter not exceeding 2 .mu.m. Further, Japanese Patent Kokai 63-130521, 5-13994 and 5-163122 teach a method in which an organopolysiloxane is used as an adjuvant of various base compositions in the form of a so-called microemulsion.
Though excellent in the stability of the aqueous emulsion and high foamability of the toiletry preparations, the above mentioned current toward the use of an aqueous organopolysiloxane emulsion having a small particle diameter of the organopolysiloxane droplets dispersed therein has a problem that, when the toiletry preparation is a hair-care treatment preparation, adherence of the organopolysiloxane to the surface of the hair treated therewith is not good enough so that the advantageous effects desired for the hair treatment is readily lost by rinse. As is taught in Japanese Patent Kokai 7-188557, this problem can be solved by the use of an aqueous organopolysiloxane emulsion of which the organopolysiloxane droplets have a relatively large particle diameter in the range from 3 to 100 .mu.m. Though suitable as an adjuvant in shampoo compositions, the aqueous organopolysiloxane emulsion disclosed there, however, has a problem that, when the emulsion is admixed with a hair-care treatment preparation, such as rinses, hair conditioners and treatments, which are sometimes formulated with a cationic surface active agent while the emulsion disclosed there is prepared by using an anionic surface active agent as the emulsifying agent, the incompatibility of the different surface active agents results in phase separation or precipitation of the ingredients so that a hair-care treatment preparation having excellent stability cannot be obtained.
With an object to solve the above mentioned problem of instability of emulsions, a proposal has been made by the inventors for the use of a cationic surface active agent as an emulsifying agent in the preparation of an aqueous organopolysiloxane emulsion. According to this proposal, the cationic surface active agent is a salt having a quaternary ammonium group in the molecule. While it is known that the stability of the aqueous organopolysiloxane emulsion prepared by using a quaternary ammonium salt as the cationic emulsifying agent can be high when the alkyl group or groups forming the quaternary ammonium group have a small number of carbon atoms to give an increased surface activity, such a lower alkyl-containing quaternary ammonium salt has an antimicrobial activity on the other side, which means that the compound is strongly irritative against human skins, mucous membranes and eyes not to be suitable as an ingredient in a toiletry preparation. This disadvantage of irritativeness against human body can at least partly be overcome by the use of a quaternary ammonium salt having at least one long-chain alkyl group with 18 or more carbon atoms. Although the adverse effect on the foamability caused by the use of a long-chain alkyl-containing quaternary ammonium salt is not so detrimental if the long-chain alkyl group has 16 carbon atoms or less, the organopolysiloxane droplets in the aqueous emulsion cannot have a particle diameter fine enough to greatly decrease the stability of the emulsion when the long-chain alkyl group in the quaternary ammonium salt has 18 carbon atoms or more.